Axle Driving Unit For A Lawn Tractor

ABSTRACT

An axle driving unit includes a pair of axles, a differential unit for differently connecting the pair of axles to each other, a hydraulic pump, a hydraulic motor, a motor shaft, an output gear on said motor shaft for drivingly connecting to said differential unit, a center section having a pump mounting surface and a motor mounting surface onto which said hydraulic pump and the hydraulic motor are mounted respectively, a housing constituted by a first housing part and a second housing part joined to each other at a joint surface, and a fastener fastening the center section to the first housing part. The center section is entirely disposed in the first housing part, whereby the hydraulic pump, the hydraulic motor and the output gear are entirely contained in the first housing part. The motor mounting surface may be disposed in parallel to the joint surface of the housing. The hydraulic pump may be located a distance from said pair of axles that is greater than a distance from the hydraulic motor to the pair of axles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/254,746, filed Oct. 21, 2005, which is a continuation of U.S.application Ser. No. 10/847,372, filed May 18, 2004, now U.S. Pat. No.6,983,815, which is a continuation of U.S. application Ser. No.10/187,848, filed Jul. 3, 2002, now U.S. Pat. No. 6,752,236, which is acontinuation of U.S. application Ser. No. 10/101,071, filed Mar. 20,2002, now U.S. Pat. No. 6,568,498, which is a continuation of U.S.application Ser. No. 08/875,724, filed Aug. 4, 1997, now U.S. Pat. No.6,390,227, which is a National Stage of PCT International No.PCT/US95/04097, filed Mar. 30, 1995, the entire disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an axle driving unit suitable for usewith a rear-discharge lawn tractor having a mower located beneath thebody of the tractor between the front and rear wheels.

2. Related Art

U.S. Pat. No. 3,969,876 discloses a conventional lawn tractor having arear discharge system, which has a mower driven by a prime mover mountedon it, and a leaf blower loaded on the rear portion of the tractor. Therear discharge system disposes a chute, for discharging lawn grass cutby the mower, longitudinally between the left and right rear wheels. Therear discharge system has no projection to the outside of the body ofthe tractor. The cut lawn grass is discharged directly rearwardly of thetractor. This has the advantage of eliminating equipment, such as anauxiliary suction fan.

However, because the space between the left and right rear wheels isvery narrow, it is very difficult to laterally juxtapose therebetweenthe cut grass chute and an axle driving apparatus. As disclosed in U.S.Pat. No. 3,969,876, a hydraulic stepless speed change transmission and adifferential gear constituting the axle driving unit are separated andare housed in separate housings. The differential gear is disposed inthe narrow space between the wheels, and the transmission is disposed atanother position on the body of the tractor. The output shaft of thehydraulic stepless speed change transmission and differential gear areconnected by a chain belt mechanism. Accordingly, the axle driving unithas the disadvantages of a high manufacturing cost and a long assemblytime. Also, since one axle, through which the cut grass chute passes, ismuch longer than the other axle, this design has the furtherdisadvantage that the one longer axle is easy to deflect. Accordingly,the lifespan of a bearing for the one longer axle provided at thedifferential gear is reduced.

An axle driving unit which houses in a common housing a hydraulicstepless speed change transmission and a differential gear fordifferentially connecting a pair of axles and integrates them iswell-known, as disclosed in, for example, U.S. Pat. No. 4,914,907 andNo. 4,932,209. In these patents, the transmission comprises acombination of a variable displacement type hydraulic pump and a fixeddisplacement hydraulic motor. The hydraulic pump and motor are mountedside by side and longitudinally of the axle with respect to anL-like-shaped center section, whereby the entire axle driving unit islarger in width longitudinally of the axle. Hence, the axle driving unitof this design interferes with the chute of a lawn tractor which has arear discharge system. As a result, the chute cannot be disposed betweenthe left and right rear wheels.

SUMMARY OF THE INVENTION

The axle driving unit of the present invention is constructed so that afirst shorter axle that mounts a first driving wheel, and a secondlonger axle that mounts a second driving wheel are supported by ahousing provided on a body frame. The housing is attached to the tractorbody frame so that it is eccentric or offset to be in proximity to thefirst driving wheel. The housing is provided with an enlarged regionextending forward at approximately a right angle with respect to theaxles. A hydraulic stepless speed change transmission is provided in theenlarged region. As a result, the axle driving unit of the presentinvention can be easily disposed laterally of (or to the side of) thechute of a lawn tractor of the rear discharge type.

In order to improve the operating efficiency of the hydraulic steplessspeed change transmission, it is desirable to construct the transmissionso that it is a hydraulic stepless system fluidly connecting thehydraulic pump and hydraulic motor to each other. In this case, thehydraulic pump can be disposed in the enlarged region, smaller in widthand spaced apart from the axle, and the hydraulic motor can be disposedin proximity to the axle.

In the enlarged region are provided a pump mounting surface and a motormounting surface disposed substantially perpendicular or rectangularwith respect to each other for mounting the hydraulic pump and hydraulicmotor. It is preferable that the hydraulic pump is mounted onto the pumpmounting surface so that an input shaft connected to the hydraulic pumpis oriented approximately vertically with respect to the axles, and thehydraulic motor is mounted onto the motor mounting surface so that anoutput shaft connected to the hydraulic motor is oriented approximatelyhorizontally with respect to the axles. In a lawn tractor that includesa prime mover having a vertical crankshaft, the input shaft of thetransmission can be connected therewith by use of a simple belttransmitting mechanism. The output shaft of the transmission can beconnected with the axle by use of an inexpensive spur gear having a lowmanufacturing cost.

Bearing means are provided in the housing for supporting the first andsecond axles. A pair of bearing holding portions for supporting distalportions of the first and second axles define the width of the housingto be smaller than the length of the housing including the enlargedregion. As a result, the enlarged region is elongated so that the chutecan have as large a cross-sectional area as possible.

It is desirable that the second longer axle be supported at anintermediate portion thereof by a bearing device provided on the tractorbody frame. As a result, the second longer axle is stably supported. Itis also desirable that the second axle be composed of at least two axleparts separably connected with each other through a coupling. Hence, theaxle driving unit becomes superior in assembly efficiency andtransformation efficiency. The axle to which the other (first) drivingwheel is mounted is stably supported by a bearing device provided on thetractor body frame.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a side view of a lawn tractor of the present invention.

FIG. 2 is a cross sectional view of the lawn tractor of FIG. 1 takenalong line 2-2.

FIG. 3 is a cross sectional view taken along line 3-3 in FIG. 2.

FIG. 4 is a cross sectional view taken along line 4-4 in FIG. 3 showinga first embodiment of the axle driving unit, from which an upper halfhousing is removed.

FIG. 5 is a sectional view taken on the line 5-5 in FIG. 4.

FIG. 6 is a sectional view taken on the line 6-6 in FIG. 4.

FIG. 7 is a sectional view taken on the line 7-7 in FIG. 4.

FIG. 8 is a sectional view taken on the line 8-8 in FIG. 4.

FIG. 9 is a sectional view taken on the line 9-9 in FIG. 8.

FIG. 10 is a sectional view taken on the line 10-10 in FIG. 4.

FIG. 11 is a perspective view of a center section of the presentinvention.

FIG. 12 is a partially sectional plan view of a second embodiment of theaxle driving unit, from which an upper half housing is removed.

FIG. 13 is a sectional view taken on the line 13-13 in FIG. 12.

FIG. 14 is a sectional view taken on the line 14-14 in FIG. 12.

FIG. 15 is a sectional view taken on the line 15-15 in FIG. 12.

FIG. 16 is a perspective view of a center section of the secondembodiment.

FIG. 17 is a partially sectional plan view of a third embodiment of theaxle driving unit, from which an upper half housing is removed.

FIG. 18 is a sectional view taken on the line 18-18 in FIG. 17.

FIG. 19 is a perspective view of a center section of the thirdembodiment.

FIG. 20 is a sectional side view of a fourth embodiment of the axledriving unit.

FIG. 21 is a sectional plan view taken on the line 21-21 in FIG. 20.

FIG. 22 is a sectional front view taken on the line 22-22 in FIG. 21.

FIG. 23 is a sectional side view of a fifth embodiment of the axledriving unit.

FIG. 24 is a sectional plan view taken on the line 24-24 in FIG. 23.

FIG. 25 is a sectional front view taken on the line 25-25 in FIG. 23.

FIG. 26 is a sectional side view of a sixth embodiment of the axledriving unit.

FIG. 27 is a sectional plan view taken on the line 27-27 in FIG. 26.

FIG. 28 is a sectional front view taken on the line 28-28 in FIG. 26.

FIG. 29 is a sectional side view of a seventh embodiment of the axledriving unit.

FIG. 30 is a sectional plan view taken on the line 30-30 in FIG. 29.

FIG. 31 is a sectional front view taken on the line 31-31 in FIG. 29.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of the various embodiments, description ofparts designated with the same reference numerals will not be repeated,unless specifically noted otherwise. In FIGS. 1 through 3, a lawntractor of the present invention is so constructed that an engine E isloaded on the front of a body frame 1, and left and right freelysteerable driven (or front) wheels 2 are suspended under the front ofthe body frame. An axle driving unit provided with left and rightdriving (or rear) wheels 3L and 3R is suspended at the rear of bodyframe 1. A grass catcher 4 is mounted to the rear end of body frame 1,and a mower 5 is attached beneath the body of the tractor between thefront and rear wheels through an elevation device (not shown). Mower 5is connected at a rear discharge port 5 a thereof with an inlet port ofcatcher 4 through a chute 6. Chute 6 extends slantwise upwardly from therear discharge port 5 a of the mower 5, passes laterally or to the sideof the axle driving unit and between the left and right rear drivingwheels 3L and 3R, and is connected to the inlet of catcher 4.Accordingly, lawn grass cut by mower 5 is blown rearwardly to passbetween left and right rear driving wheels 3L and 3R through chute 6,and is then stored in catcher 4. The lawn tractor preferably includes aheight-adjustable seat that can be raised and lowered.

As shown in FIG. 1, two pulleys 8 and 9 are fixed onto an output shaft 7of engine E. Pulley 8 transmits a driving force through a belt 10 to athird pulley 12 fixed onto an input shaft 11 of mower 5, therebyrotating cutter blades 5 b of mower 5 (see FIG. 2). The other pulley 9is adapted to transmit a driving force through a belt 13 to a fourthpulley 15 fixed onto a pump shaft or input shaft 29, projecting upwardlyfrom a housing for the axle driving unit. Reference numeral 16designates a cooling fan fixed to pulley 15 in order to cool the axledriving unit.

As shown in FIG. 3, the axle driving unit is suspended from a firstmounting member 1 a and a second mounting member 1 b, both parts of bodyframe 1. The axle driving unit is eccentrically disposed toward one ofthe two sides of body frame 1. FIG. 3 shows the axle driving unitdisposed in a position displaced toward driving wheel 3L relative to thecenter of the space between left and right driving wheels 3L and 3R. Theleft side of the housing of the axle driving unit is fixed to firstmounting member 1 a, and the right side to second mounting member 1 bthat downwardly extends from a laterally intermediate portion of firstmounting member 1 a. As shown in FIG. 3, body frame 1 of the tractorincludes first mounting member 1 a provided longitudinally of body frame1 and at a portion adjacent to the inside of driving wheel 3L. Thesecond mounting member 1 b is suspended from about the center of thespace between driving wheels 3L and 3R. A bearing 20 is provided at aportion of body frame 1 adjacent to the inside of driving wheel 3R.

The housing for the axle driving unit comprises an upper half housing 21and a lower half housing 22 joined to each other through a peripheraljoint or junction surface. When the housing is mounted in an operatingposition on body frame 1 of the tractor, the joint surface issubstantially horizontally disposed.

Shorter first axle 17 projects from the left side of the housing for theaxle driving unit, and longer second axle 18 projects from the rightside of the housing. Driving wheel 3L mountsat one axial end of firstaxle 17, and driving wheel 3R mounts at one axial end of second axle 18.

A first mounting boss 210 a is formed at a portion of the axle drivingunit housing positioned near the distal portion (portion closest to theaxle driving unit) of first axle 17, and a second mounting boss 210 b isformed at the portion of the housing positioned near the distal portionof second axle 18.

First mounting member 1 a is connected to first mounting boss 210 a, andsecond mounting member 1 b is connected to second mounting boss 210 b.Thus, the housing is eccentrically mounted in the working or operatingposition, offset to one side toward driving wheel 3L. Such a layoutensures a sufficiently wide space between the axle driving unit housingand driving wheel 3R so that chute 6 can be offset from the center ofthe tractor body. As a result, the axle driving unit and chute 6 can bearranged laterally, side by side each other within body frame 1. Thisenables chute 6 to longitudinally extend within body frame 1.

Second axle 18 is supported at the distal portion thereof (18 a) by thehousing, and at an intermediate portion of a longer portion (18 b)projecting outwardly from the housing by a bearing 20. Hence, thedistance between the bearing for supporting the distal portion of firstaxle 17 and that for supporting the distal portion of second axle 18 canbe greatly reduced, thereby reducing the width W of the axle drivingunit housing. Consequently, chute 6 can be designed with a relativelyincreased cross-sectional area.

Alternatively, second axle 18 may be formed as one long axle. However,it is favorable for assembly of the axle driving unit and facilitationof transportation to divide axle 18 into part 18 a supported at thehousing, and part 18 b supported by bearing 20, as shown in FIG. 3.Parts 18 a and 18 b are connected by a coupling 19.

FIGS. 4-11 show the construction of an axle driving unit forspeed-change-driving rear driving wheels 3L and 3R. The housing of theaxle driving unit is formed by connecting upper half housing 21 andlower half housing 22 with each other. Lubricating oil is charged intothe housing; and is used as operating oil for a hydraulic stepless speedchange transmission T to be discussed below. First axle 17 and part 18 aof the second axle are rotatably supported in upper half housing 21positioned above the joint surface. As shown in FIG. 10, cylindricalbores 211 are formed at left and right side walls of upper half housing21 to form first bearing supports, respectively. Rolling bearings 100fitted into cylindrical bores 211 support the distal portion of firstaxle 17 and part 18 a of second axle 18, cylindrical bores 211 beingclosed at their outer ends with oil seals.

As best seen in FIG. 10, semicircular concave circular-arc surfaces 212are formed on the inner surface of an upper wall of upper half housing21. On the inner surface of lower half housing 22 are integrally formedprojections 220 that project beyond the joint surface. Semicircularconcave circular-arc surfaces 221 are formed at the end surfaces ofprojections 220 that are positioned opposite to concave surfaces 212,respectively, to form a pair of second bearing holders. Bushings 101 areinserted into the second bearing holders, so that bushings 101 supportthe base ends of first axle 17 and part 18 a of second axle 18,respectively.

As shown in FIG. 10, concave circular-arc surfaces 213 larger in radiusthan surfaces 212 are formed in concave circular-arc surfaces 212, andconcave circular-arc surfaces 222 larger in radius than surfaces 221 areformed in concave circular-arc surfaces 221. Concave circular-arcsurfaces 213 and 222 are combined to form annular cavities. Rollingbearings (not shown) may be built-in to the cavities, instead of theaforesaid bushings 101, to support the base ends of first and secondaxles 17 and 18. The choice of bushings or bearings depends upon thesize of the load applied to axles 17 and 18. When the load is small,bushings 101, as shown in the embodiment of FIG. 10, are used to reducemanufacturing cost. When the load is large, the rolling bearings (notshown) are used to increase the support strength for the axles.

As shown in FIG. 10, first axle 17 and part 18 a of second axle 18 abutconcentrically against each other in the housing, differentiallyconnected to each other by a differential gear 23 contained in thehousing. Axle 17 and part 18 a of axle 18 project laterally outwardlyfrom the housing.

As best seen in FIGS. 8 and 10, an input gear 48 larger in width thandifferential gear 23 has at the center a through-bore 480. The base endsof first axle 17 and part 18 a of second axle 18 are inserted intothrough-bore 480 to be supported by input gear 48. Bevel gears 49,spline-engaged with first axle 17 and part 18 a of second axle 18, andinput gear 48 prevent axial movement of the axles. Pinions 50 engageablewith bevel gears 49, and through-bores 481 for containing thereinpivotal pins 51 for pinions 50, are provided at both sides of input gear48. A flat portion formed at the circumferential surface of the end ofeach pivotal pin 51 abuts against a flat portion provided at eachthrough-bore 481, thereby restraining each pivotal pin 51 from rotating.Accordingly, differential gear 23 is formed from a smaller number ofparts.

The front portions (portions toward the front or forward end of the lawntractor) of upper and lower half housings 21 and 22 are enlarged in adirection perpendicular to the longitudinal axes of the axles. Thehousing of the axle driving unit is therefore longer (length L1) than itis wide (width W; see FIG. 4). A center section 25 for a hydraulicstepless speed change transmission T is mounted in the enlarged region.As shown in FIG. 11, center section 25 is a single and elongated piecehaving an upper surface 250 and a side surface 251 which are adjacentand perpendicular to each other.

A pump mounting surface 40 is formed at the front portion (toward thefront or forward end of the lawn tractor) of upper surface 250 formounting thereon a hydraulic pump. At the rear portion of side surface251 a motor mounting surface 41 is formed for mounting a hydraulicmotor. As shown in FIG. 8, pump mounting surface 40 and motor mountingsurface 41 are partially overlapped with each other by a longitudinallength OL. The center of motor mounting surface 41 extends in parallelto pump mounting surface 40 and is offset downwardly therefrom by aheight H1.

As shown in FIG. 11, housing mounting faces 42 are formed on uppersurface 250 of center section 25, approximately level with mountingsurface 40. Therefore, housing mounting faces 42 can be ground when pumpmounting surface 40 is ground, so that the processing time for the pumpmounting surface can be reduced. Bolt insertion bores are provided athousing mounting faces 42 and center section 25 is fixed to the innerwall of the enlarged region of upper half housing 21 through connectingbolts inserted into the bores. Pump mounting surface 40 of centersection 25 extends horizontally with respect to the axles, and isdisposed spaced apart from the axles. Motor mounting surface 41 extendsvertically with respect to the axles, and is disposed in proximity tothe axles.

Alternatively, pump mounting surface 40 and motor mounting surface 41may be provided integral to the inner wall by increasing the thicknessof the inner wall in the enlarged region of lower half housing 22.However, as shown in this embodiment, it is preferable to use centersection 25 separate from the housing to facilitate processing of thehousing, and to prevent oil from leaking out of the housing.

As shown in FIG. 5, a valve plate 102 is mounted onto pump mountingsurface 40. A cylinder block 36, constituting the hydraulic pump, isrotatably disposed on valve plate 102. Pistons 36 a are fitted into aplurality of cylinder bores of cylinder block 36, for reciprocatingmovement through biasing springs. Pump shaft 29 engages with a splinebore provided on the rotary axis of cylinder block 36. Pump shaft 29 isrotatably supported by upper half housing 21 and pump mounting surface40. Pulley 15 is fixed to a projection of pump shaft 29 projectingoutwardly from upper half housing 21. The heads of pistons 36 a abutagainst a thrust bearing 28 a of a movable swash plate 28, therebyforming an axial piston type variable displacement hydraulic pump.Alternatively, the hydraulic pump may be of a radial piston type or agear type.

Pump shaft 29 is inserted into a longitudinally extending through-boreformed at the axial center of movable swash plate 28. A convexcircular-arc surface is formed at the rear of movable swash plate 28,and slidably contacts with a concave circular-arc surface formed at theinner surface of the upper wall of upper half housing 21. As a result,movable swash plate 28 is movable in a longitudinal slantwise directionalong the concave circular-arc surface. As movable swash plate 28 moveswith respect to the rotary axis of cylinder block 36 along the contactsurface, the amount and flow direction of oil discharged from thehydraulic pump changes. As shown in FIG. 5, a control shaft 35 formovably operating movable swash plate 28 extends horizontally and isrotatably supported by a lid 38 that closes a side opening of upper halfhousing 21. At an outer end of control shaft 35 is fixed a control lever35 a that is connected in association with a speed change operating tool(not shown). At an inner end of control shaft 35 is fixed a base of aswinging arm 35 b. A ball 37, fixed to the utmost end of swinging arm 35b, engages through a joint block with an engaging groove 28 b of movableswash plate 28, control shaft 35 being rotated for movement of movableswash plate 28.

Movable swash plate 28 shown in this embodiment is of a cradle type thatmoves slantwise along the concave circular-arc surface of the innersurface of the upper wall of upper half housing 21. To enable atrunnion-type swash plate to be mounted instead of cradle-type swashplate 28, a bearing bore is positioned on the same axis as control shaft35 at a portion of the inner wall of upper half housing 21. Where thetrunnion-type movable swash plate is used, each trunnion shaft issupported by the bearing bore and lid 38. The cradle-type movable swashplate is advantageous in that it is inexpensive to produce, while thetrunnion-type is advantageous in that it requires a decreased operatingforce. Swash plates of both types are easily exchangeable.

Referring to FIG. 6, a valve plate 103 is mounted onto motor mountingsurface 41 formed on side surface 251 of center section 25. A cylinderblock 44 of the hydraulic motor is rotatably disposed on plate 103. Aplurality of pistons 44 a are fitted for reciprocating movement into aplurality of cylinder bores of cylinder block 44.

The heads of pistons 44 a abut against a thrust bearing 45 a at a fixedswash plate 45, fixed between upper half housing 21 and lower halfhousing 22. A motor shaft 24 engages with a spline bore provided on therotary axis of cylinder block 44 to form an axial-piston type fixeddisplacement hydraulic motor. Alternatively, the hydraulic motor may beof a radial piston type or a gear type.

The rotation axis of cylinder block 44 is positioned in the same planeas the joint surface of the upper and lower half housings. One end ofmotor shaft 24 is supported by motor mounting surface 41, the other endbeing supported by a bearing sandwiched between upper half housing 21and lower half housing 22.

When the hydraulic pump and the hydraulic motor are disposed on a centersection having the configuration described above, pump shaft 29 andmotor shaft 24 are perpendicular to each other. Pump shaft 29 is offsetfrom motor shaft 24 by a length L2 in the direction apart from the axles(see FIG. 8).

As shown in FIGS. 4, 9, and 11, a pair of kidney-shaped ports 40 a and40 b is open on pump mounting surface 40 of center section 25 to take inor discharge oil in cylinder block 36. A pair of kidney-shaped ports 41a and 41 b is also open on motor mounting surface 41 to take in ordischarge oil in cylinder block 44. Within center section 25 areprovided a straight oil passage 25 a and an L-like-shaped oil passage 25b for connecting kidney-shaped ports 40 a and 41 a, and 40 b and 41 bwith each other, respectively, to circulate the operating oil betweenthe hydraulic pump and hydraulic motor, thereby making a closed circuit.

The hydraulic pump and hydraulic motor are fluidly connected with eachother through the above-mentioned closed circuit, and the combination ofthese members forms a hydraulic stepless speed change transmission.Capacity of the hydraulic pump is changed by rotatably operating controllever 35 a, thereby enabling the hydraulic motor to obtain steplessoutput rotation.

Operating oil supply means is provided for replenishing oil that hasleaked out from center section 25. The supply means may be the hydraulicpump itself, or a charge pump 31.

Charge pump 31, as shown in FIGS. 5 and 7, is a trochoid pump which iscontained in a charge pump casing 30 attached to a charge pump mountingsurface 43 formed on the lower surface of center section 25. A wavewasher 34 is interposed between a stepped portion at the outer peripheryof charge pump casing 30, and a bottom surface of a lid 33 that closesan opening 223 in lower half housing 22. Wave washer 34 biases chargepump 31 so that charge pump 31 is in contact with charge pump mountingsurface 43. The lower end of pump shaft 29 passes through center section25 and projects from charge pump mounting surface 43, and a pin ismounted on shaft 29. An engaging bore is open at the center of aninternal gear of charge pump 31. The lower end of pump shaft 29 isinserted into the engaging bore, and pump shaft 29 engages with theinternal gear. Charge pump 31 is fixed to the lower end of pump shaft 29and is driven by pump shaft 29.

Charge pump casing 30 is disposed in an oil sump formed by the housing.A suction port 30 a of charge pump 31 is open at the lower surface ofcharge pump casing 30. Suction port 30 a connects with the oil sump inthe housing through a groove 33 a formed by partially cutting out a wavewasher mounting portion at lid 33. An annular oil filter 32 is fixedbetween charge pump mounting surface 43 and the bottom surface of lid33. Since oil filter 32 surrounds charge pump 31 and charge pump casing30, existing oil is cleaned and then taken in by charge pump 31 throughgroove 33 a and suction port 30 a. When oil filter 32 is maintained andinspected, lid 33 is removed from lower half housing 22, and oil filter32 is removed from the housing through an opening 223 of lower halfhousing 22, oil filter 32 being smaller in outline than opening 223.

The pressure oil discharged from charge pump 31 is directly guided intoa supply oil passage 25 c open in charge pump mounting surface 43. Ifthe introduced pressure exceeds the pressure corresponding to a biasingforce of the wave washer biasing means, the pressure causes charge pumpcasing 30 to move away from or detach from charge pump mounting surface43 against the biasing force of wave washer 34. This creates a gapbetween charge pump 31 and charge pump mounting surface 43. Pressure oilis then released in part from the gap into the oil sump to adjust itspressure below the biasing force of wave washer 34. Charge pump 31 isdetached from charge pump mounting surface 43 to adjust the dischargepressure below the biasing force while maintaining fluid communicationbetween the discharge port and the oil supply port.

As shown in FIG. 8, due to the form of center section 25, pump mountingsurface 40 is positioned in the second plane P2 in upper half housing21, in parallel to and spaced apart by a height H1 from the first planeP1 coincident with the joint surface of the housing. Hence, a wide spaceis formed between charge pump mounting surface 43 positioned opposite topump mounting surface 40, and the inner surface of the bottom of lowerhalf housing 22. As a result, charge pump 31 and oil filter 32 can becontained in this space with ample room. Height H2 from the axis of theaxles to the bottom of lower half housing 22 is reduced to ensuresufficient ground clearance.

As shown in FIG. 9, check valves 50 are disposed at the open ends of oilpassages 25 a and 25 b in the closed circuit of center section 25. Checkvalves 50 mutually communicate at the inlet ports through one transversepassage 25 d. Transverse oil passage 25 d communicates at theintermediate portion with a supply oil passage 25 c open at charge pumpmounting surface 43 of center section 25. Oil introduced from thedischarge port of charge pump 31 to supply oil passage 25 c reaches theinlet side of each check valve 50. The oil pressure pushes out checkvalves 50, positioned at the low pressure side of oil passages 25 a and25 b, so that oil is supplied from the outlet side into the closedcircuit.

Check valves 50 are slidably provided with push pins 51 that projectoutward from center section 25. An axial end of each push pin 51 comesin contact with a single connecting plate 52 in the housing, and arelease rod 53 is fixed at the center of connecting plate 52. Releaserod 53 projects outwardly from upper half housing 21 at one end.Connecting plate 52 is outwardly biased by a spring 54 interposedbetween plate 52 and center section 25. Release rod 53 is manuallypushed in, so that push pins 51 simultaneously push out check valves 50so that the inlet port is in fluid communication with the outlet port.Hence, oil passages 25 a and 25 b communicate with each other throughtransverse oil passage 25 d, thereby enabling the hydraulic motor toidle.

As shown in FIGS. 4 and 8, motor shaft 24 is disposed in parallel toaxles 17 and 18. A counter shaft 26 is provided between the axles andmotor shaft 24, and extends in parallel to the axles and motor shaft 24.A gear 240 is provided on motor shaft 24 and engages with a largerdiameter gear 46 fixed onto counter shaft 26. A smaller diameter gear 47on counter shaft 26 engages with a ring gear 48 of differential gear 23.Thus, a driving force output from motor shaft 24 is transmitted to axles17 and 18 through a gear system speed reduction transmission anddifferential gear 23.

As shown in FIG. 4, a braking friction plate 63 is fixed on motor shaft24, an arm 64 is fixed to upper half housing 21, and a brake actuator 65is provided at one end of arm 64. An operating lever (not shown) isrotated to bring brake actuator 65 in press contact with brakingfriction plate 63, thereby enabling motor shaft 24 to be braked.

The axis of counter shaft 26 is positioned in the first plane P1. It issupported at both axial ends by a pair of bearings interposed betweenupper half housing 21 and lower half housing 22.

As shown in FIG. 8, a pocket projects from the bottom of lower halfhousing 22 to define height H2. The lower portion of larger diametergear 46 on counter shaft 26 is contained within this pocket.

The axes of axles 17 and 18 may be disposed in the first plane P1.However, it is preferable to dispose the axes above the first plane P1as shown in this embodiment. This is because, even when a large diameterinput gear 48 is used in order to enlarge the last gear ratio, the lowerportion of input gear 48 will not extend lower than the lower portion oflarger diameter gear 46. Therefore, the pocket for gear 46 need not befurther enlarged, thereby enabling height H2 to be as small as possibleso that ground clearance is ensured.

As shown in FIG. 4, differential gear unit 23 is displaced in thehousing toward part 18 a of second axle 18. A space is thereby formed atone lateral side of a second axle holder. The larger diameter gear 46 ispartly disposed in this space so that the length of the housing does nothave to be increased. As shown in FIG. 8, a partition 214 for coveringan upper portion of input gear 48 is integrally formed in upper halfhousing 21 and an oil flow-through bore 215 is formed at partition 214.An opening 216 is formed at a portion of the upper wall of upper halfhousing 21 positioned above partition 214, and covered with a covermember 55. Cover member 55 is provided with a breather 56 and an oilcheck rod 57 that is also used as an oil charge plug. A predeterminedamount of oil is charged into the housing through cover member 55 sothat the boundary of oil and air is formed in a space enclosed bypartition 214 and cover member 55. Air mixed in the oil when chargedinto the housing is collected in an air reservoir through oilflow-through bore 215. Partition 214 is filled at the lower portion withoil, so that, even when the various gears rotate, the air in the airreservoir is scarcely mixed in the oil. When the axle driving unit isoperated for a long time, the oil volume expands. The volume of air inthe air reservoir decreases to accommodate the expanded volume of oil.

A second embodiment of the axle driving unit is shown in FIGS. 12-16.The second embodiment is almost the same in construction as the firstembodiment so that the same parts are designated with the same referencenumerals and the description is omitted. As such, only three points ofdifferent construction will be described.

In the case where a lawn tractor includes a wide space underneath thetractor where the mower is disposed, the enlarged region of the housingis extended forwardly as much as possible. The width of the housing ismade as small as possible, thereby enabling the grass chute to increasein volume.

Therefore, a first difference is to elongate the enlarged region of thehousing, and to suitably form center section 25 for such an enlargedregion. Pump mounting surface 40 and motor mounting surface 41, formedon upper surface 250 and side surface 251 of center section 25, areformed so that motor mounting surface 41 laterally overlaps pumpmounting surface 40. As a result, center section 25 can be contained inthe enlarged region having width Wa (see FIG. 12). Cylinder block 36 ofthe hydraulic pump is disposed further away from axles 17 and 18 than inthe first embodiment. Length L2 from pump shaft 29 to motor shaft 24 islarger in this embodiment (see FIG. 13) than in the first embodiment(see FIG. 8). There is no overlap OL in this embodiment as there was inthe first embodiment (see FIG. 8).

A third mount boss 210 c is provided at the utmost end of the enlargedregion of the housing. Mount boss 210 c is connected to a third mountingmember (not shown) hanging from body frame 1. Therefore, even when theentire length L1 of the housing becomes larger, the axle driving unitremains in a proper operating position.

A second difference is with respect to motor shaft 24. As in the firstembodiment, braking friction plate 63 is disposed on one end of motorshaft 24 that extends outwardly from the housing. The difference in thisembodiment is that the other end of motor shaft 24 is provided with aspline, and it extends into a through-open bore provided at the centerof motor mounting surface 41. A bushing is interposed between the jointsurfaces of the housing to support a rotary shaft 59 (see FIG. 12). Thespline end of motor shaft 24 is spline-engaged with one end of rotaryshaft 59 so that the driving force of motor shaft 24 is taken out of thehousing through rotary shaft 59.

The outer end of rotary shaft 59 is an indented spline. Braking frictionplate 63 may be mounted on this end of rotary shaft 59, or rotary shaft59 may be used as a power take-out shaft. If such construction is notrequired, rotary shaft 59 can be removed and the bore formed at thejoint surfaces of the housing can be closed by a seal cap.

A third difference is found in the movable swash plate of the hydraulicpump. Movable swash plate 60 of a trunnion-type is used in place of thatof a cradle-type. One trunnion shaft 60 a of movable swash plate 60 issupported by a lid 38 mounted to upper half housing 21, the othertrunnion shaft 60 b being supported by a bearing bore provided at theinner wall of upper half housing 21 (see FIG. 14). Trunnion shaft 60 aprojects outwardly from lid 38 and a control lever 35 a is mounted ontothe projection.

A third embodiment of the axle driving is shown in FIGS. 17-19. Theconstruction of the third embodiment compares to that of the secondembodiment as follows.

Center section 25 is not connected to upper half housing 21 by bolts,but inserted in part between upper half housing 21 and lower halfhousing 22. Therefore, center section 25 is positioned in the enlargedregion in a free-standing state. Housing mounting faces 42′ project fromthe left and right side surfaces 251. The upper surface of centersection 25 and the lower surface opposite thereto form housing mountingfaces. Since center section 25 is free-standing, bolts are not requiredso that assembly is simplified and manufacturing cost is lowered.

In order for center section 25 to be free-standing, pump shaft 29 andmotor shaft 24 are completely supported by the housing. Upper end ofpump shaft 29 is supported by a bearing 104 attached to upper halfhousing 21. Lower end of pump shaft 29 passes through mounting surface40 and charge pump mounting surface 43 and is supported by a bearing 105attached to lower half housing 22 (see FIG. 18). Motor shaft 24 passesthrough motor mounting surface 41 and the two ends are supported bybearings 106 and 107 inserted between both upper half and lower halfhousings 21 and 22 (see FIG. 17).

In the axle driving unit of an embodiment to be discussed below, as inthe second and third embodiments, the enlarged region is made aselongated as possible in order to allow greater volume for the chute ofthe rear discharge lawn tractor.

A fourth embodiment of the axle driving unit will be described inaccordance with FIGS. 20, 21 and 22. A center section 25 ofsubstantially L-like shape in sectional side view is disposed in anelongated enlarged region extending across upper half housing 21 andlower half housing 22, and is fixed to upper half housing 21. A pumpmounting surface 40 is formed on a substantially horizontal uppersurface 250, and a motor mounting surface 41 on a substantially verticalside surface 251 of center section 25. Pump mounting surface 40 ispositioned apart from axles 17 and 18, and motor mounting surface 41 ispositioned near the axles. Pump shaft 29 extends substantiallyvertically with respect to axles 17 and 18, and motor shaft 24 extendssubstantially horizontally with and perpendicular to axles 17 and 18.

A movable swash plate 60 at the hydraulic pump is of a cradle-type anduses the same operating mechanism as that in the first embodiment sothat it is manually controllable along a concave circular-arc surface ofan inner wall of upper half housing 21.

An oil filter 32 is interposed between the lower surface of centersection 25, opposite to pump mounting surface 40, and the inner surfaceof the bottom wall of lower half housing 22. Oil in the housing isfiltered by oil filter 32 and guided to a supply port (not shown) openat the lower surface of center section 25.

A pair of kidney-shaped ports 40 a and 40 b open at pump mountingsurface 40, and a pair of kidney-shaped ports 41 a and 41 b open atmotor mounting surface 41 are connected with each other through a pairof substantially L.-like-shaped oil passages 25 a and 25 b,respectively. As shown in FIG. 9, check valves are disposed at the openends of oil passages 25 a and 25 b. In this embodiment, operating oil issupplied by operation of the hydraulic pump itself, but a charge pump asdescribed in the previous embodiments may alternatively be used.

The axis of motor shaft 24 is positioned in the same plane as the jointsurface of the housing. Motor shaft 24 is rotatably supported bybearings interposed between upper half housing 21 and lower half housing22.

First axle 17 and part 18 a of second axle 18 are rotatably supported bylower half housing 22. Distal portions of first axle 17 and part 18 a ofsecond axle 18 are supported by bearings 100 held into cylindrical boresof lower half housing 22. The bases of axles 17 and 18 are supported bybushings 101 disposed in lower half housing 22. Bushings 101 are fixedlyinterposed between legs 217, long enough to extend beyond the jointsurface of the housing, and the concave circular-arc surface of lowerhalf housing 22 (see FIG. 22).

Differential gear 23 is displaced toward part 18 a of second axle 18 inthe housing. Motor shaft 24 is substantially perpendicular to first axle17, and passes above axle 17 as it extends toward the rear of thehousing. The utmost end of motor shaft 24 projects from the housing, anda braking friction plate 63 is attached to the utmost end of motor shaft24.

A counter shaft 26, extending in parallel to axles 17 and 18, isdisposed at the rear of the housing. The axis of shaft 26 is positionedin the same plane as the joint surface of the housing. Shaft 26 isrotatably supported by bearings sandwiched between upper half housing 21and lower half housing 22.

Since motor shaft 24 and counter shaft 26 are substantiallyperpendicular to each other, a smaller diameter bevel gear 240 a onmotor shaft 24 and a larger diameter bevel gear 46 a, engageable withbevel gear 240 a, on counter shaft 26 are used to connect the shaftstogether in a driving manner. The driving force is transmitted from asmaller diameter gear 47 on counter shaft 26 to axles 17 and 18 througha ring gear 48 on differential gear 23.

A fifth embodiment of the axle driving unit will be described inaccordance with FIGS. 23, 24 and 25. Center section 25, disposed in anelongated enlarged region of the housing, has a substantially flat body.Center section 25 is attached to a side of upper half housing in asubstantially horizontal manner. Pump mounting surface 40 and motormounting surface 41 are formed on upper surface 250 of center section25; the former is positioned apart from axles 17 and 18 and the latteris positioned near the axles. Pump shaft 29 of the hydraulic pump andmotor shaft 24 of the hydraulic motor extend in parallel to each other,and are substantially vertical, being at a right angle to axles 17 and18.

A pair of kidney-shaped ports 40 a and 40 b open at pump mountingsurface 40, and a pair of kidney-shaped ports 41 a and 41 b open atmotor mounting surface 41 are connected to each other through a pair ofstraight oil passages 25 a and 25 b.

Movable swash plate 28 of the hydraulic pump is of a cradle-type, and ismanually controllable along the concave circular-arc surface of theinner wall of upper half housing 21 by use of an operating mechanism asin the first embodiment. A fixed swash plate 45 of the hydraulic motoris fixedly fitted into a concave formed at the inner wall of upper halfhousing 21.

Pump shaft 29 and motor shaft 24 are rotatably supported by bearingslongitudinally juxtaposed at upper half housing 21, and bearingslongitudinally juxtaposed at center section 25.

A counter shaft 26 is disposed in the same plane as the joint surface ofthe housing. A pair of bearings for supporting counter shaft 26 aresandwiched between a pair of legs 252 downwardly projecting from thelower surface opposite to motor mounting surface 41, and a pair of legs224 upwardly projecting from the inner surface of the bottom wall oflower half housing 22 (see FIG. 23). With this construction, there is noneed for a bearing holding portion for counter shaft 26 to be providedat the housing. Therefore, the width Wa of the enlarged region can befurther restricted (see FIG. 24). One end of counter shaft 26 projectsoutwardly from the housing for attachment of a braking friction plate63.

A substantially vertical motor shaft 24 passes downwardly through centersection 25. The lower end portion of motor shaft 24 is positioned justabove, and at about a right angle to, the axis of the axles (see FIG.25). A small diameter bevel gear 240 a is fixed on the lower end ofmotor shaft 24, and a larger diameter bevel gear 46 a, engageable withbevel gear 240 a, is fixed on counter shaft 26, thereby connectingshafts 24 and 26.

A driving force is transmitted from a smaller diameter gear 47 oncounter shaft 26 to a ring gear 48 of differential gear 23, differentialgear 23 being displaced toward part 18 a of axle 18 in the housing. Theaxes of axles 17 and 18 are positioned in the same plane as the jointsurface of the housing. The terminal and bore of first axle 17 aresupported only by bearing 100 and bushing 101 interposed between upperhalf housing 21 and lower half housing 22. Differential gear 23 iseccentrically disposed to further reduce the axial length of part 18 aof second axle 18 so that part 18 a of second axle 18 is supported byonly bushing 101 sandwiched between upper half housing 21 and lower halfhousing 22.

A sixth embodiment of the axle driving unit will be described inaccordance with FIGS. 26, 27 and 28. The construction is basically thesame as that of the fifth embodiment so that only the following fourpoints are described which are different from that of the fifthembodiment.

A first modified point is the position of braking friction plate 63. Theupper end of substantially vertical motor shaft 24 passes through theupper wall of upper half housing 21, and braking friction plate 63 ismounted to this upper end. This allows the braking device to be smallerand more compact because motor shaft 24 has a lower transmitting torquethan counter shaft 26. As a result, the axle driving unit becomessmaller in width. Braking friction plate 63 is disposed on the same sideas pump shaft 29 that projects from the housing, and is in proximity tocooling fan 16. This enables friction plate 63 to be effectively cooledby the ventilation from cooling fan 16. The ventilation from cooling fan16 also blows away the dust collected on braking friction plate 63.

A second modified point is with respect to center section 25. One leg252 downwardly projects from the surface of center section 25 oppositeto motor mounting surface 41. Leg 252 and lower half housing 22 supporta bearing for the end of counter shaft 26, and a bearing at the otherend of counter shaft 26 is sandwiched between upper half housing 21 andlower half housing 22. Leg 252 may be formed separately from centersection 25 and fixed below its plane.

A third modified point is with respect to differential gear 23′. Aninput gear 48′ of differential gear 23′ is freely fitted on part 18 a ofsecond axle 18, and is disposed in proximity to one side wall of thehousing, thereby considerably reducing the axial length of part 18 a ofsecond axle 18. A differential case 48 a is attached to the oppositeside wall of the housing. In differential case 48 a, the base ends offirst axle 17 and part 18 a of second axle 18 face each other. Sidegears 49 engage with pinions 50 pivoted to the base sides of first axle17 and part 18 a of second axle 18.

A fourth modified point is in the layout of first axle 17 and part 18 aof second axle 18 and the construction of the housing support withrespect to the joint surface of the housing. The axes of axles 17 and 18can be disposed in substantially the middle portion of the height of thehousing and still retain the balance of the axle driving unit. Theprotrusion formed in the bottom portion of lower half housing 22 forinput gear 48′ can thus be made smaller in volume to ensure sufficientheight from the ground.

A seventh embodiment of the axle driving unit will be described inaccordance with FIGS. 29, 30 and 31.

Center section 25, as in the fifth and sixth embodiments, issubstantially shaped like a flat plate, and mounted to upper halfhousing 21. The body of center section 25 is substantially horizontallydisposed in lower half housing 22. Pump mounting surface 40 is formed onthe substantially horizontal upper surface of center section 25 spacedapart from axles 17 and 18. Motor mounting surface 41 is formed on thesubstantially horizontal lower surface of center section 25 in proximityto axles 17 and 18.

Motor shaft 24 of the hydraulic motor is journalled at its upper end tocenter section 25, and at its lower end to lower half housing 22. If itis difficult to mount the hydraulic motor onto motor mounting surface41, the lower end of motor shaft 24 may be journalled to a fixed swashplate 45, and fixed swash plate 45 may be connected to the lower surfaceof center section 25.

Motor shaft 24 extends in parallel to pump shaft 29, and substantiallyvertically passes through the upper wall of center section 25. On theupper end of motor shaft 24 is fixed a smaller diameter bevel gear 240 aengageable with a larger diameter bevel gear 46 a on counter shaft 26.

In order to support counter shaft 26 in the same plane as the jointsurface of the housing, a pair of bearings is provided between a pair oflegs 252′, upwardly projecting from the surface of the center sectionopposite to motor mounting surface 41, and a pair of legs 218 projectingfrom the inner wall of upper half housing 21.

Although several embodiments have been described, they are merelyexemplary of the invention and not to be construed as limiting, theinvention being defined solely by the appended claims and theirequivalents.

1. An axle driving unit, comprising: a pair of axles; a differentialunit for differently connecting said pair of axles to each other; ahydraulic pump; a hydraulic motor; a motor shaft; an output gear on saidmotor shaft for drivingly connecting to said differential unit; a centersection having a pump mounting surface and a motor mounting surface ontowhich said hydraulic pump and said hydraulic motor are mountedrespectively so as to be fluidly connected with each other through saidcenter section; a housing being constituted by a first housing part anda second housing part joined to each other at a joint surface, afastener fastening said center section to said first housing part,wherein said center section is entirely disposed in said first housingpart, whereby said hydraulic pump, said hydraulic motor and said outputgear are entirely contained in said first housing part, wherein saidmotor mounting surface is disposed in parallel to said joint surface ofsaid housing.
 2. The axle driving unit as set forth in claim 1, whereinsaid fastener is a bolt, and wherein longitudinal directions of saidmotor shaft and said bolt are parallel to each other.
 3. The axledriving unit as a set forth in claim 1, further comprising a pump shaftwhose longitudinal direction is parallel to a longitudinal direction ofsaid motor shaft.
 4. The axle driving unit as set forth in claim 1,wherein a longitudinal direction of said motor shaft is perpendicular toa longitudinal direction of said pair of axles.
 5. The axle driving unitas set forth in claim 1, wherein said differential unit furthercomprising: an input gear to receive the torque of said motor shaft; aplanetary gear for transmitting the rotation of said input gear to saidpair of axles; and a pivot pin for pivoting said planetary gear, whereinsaid pivot pin is directly supported by said input gear.
 6. The axledriving unit as set forth in claim 1, wherein most of said differentialunit is entirely disposed in said first housing part.
 7. The axledriving unit as set forth in claim 1, wherein said joint surface isparallel to a plane located at a rotational axis of the axles.
 8. Anaxle driving unit, comprising: a pair of axles; a differential unit fordifferently connecting said pair of axles to each other; a hydraulicpump; a hydraulic motor; a motor shaft; an output gear on said motorshaft for drivingly connecting to said differential unit; a centersection having a pump mounting surface and a motor mounting surface ontowhich said hydraulic pump and said hydraulic motor are mountedrespectively so as to be fluidly connected with each other through saidcenter section; a housing being constituted by a first housing part anda second housing part joined to each other at a joint surface, afastener fastening said center section to said first housing part,wherein said center section is entirely disposed in said first housingpart, whereby said hydraulic pump, said hydraulic motor and said outputgear are entirely contained in said first housing part, wherein saidhydraulic pump is located a distance from said pair of axles that isgreater than a distance from said hydraulic motor to said pair of axles.9. The axle driving unit as set forth in claim 8, wherein said fasteneris a bolt, and wherein longitudinal directions of said motor shaft andsaid bolt are parallel to each other.
 10. The axle driving unit as a setforth in claim 8, further comprising a pump shaft whose longitudinaldirection is parallel to a longitudinal direction of said motor shaft.11. The axle driving unit as set forth in claim 8, wherein alongitudinal direction of said motor shaft is perpendicular to alongitudinal direction of said pair of axles.
 12. The axle driving unitas set forth in claim 8, wherein said differential unit furthercomprising: an input gear to receive the torque of said motor shaft; aplanetary gear for transmitting the rotation of said input gear to saidpair of axles; and a pivot pin for pivoting said planetary gear, whereinsaid pivot pin is directly supported by said input gear.
 13. The axledriving unit as set forth in claim 8, wherein most of said differentialunit is entirely disposed in said first housing part.